Leica M3

The Leica M3 was introduced in 1954. It was a new starting point for Leitz, which until then had only produced screw-mount Leica cameras that were incremental improvements to its original Leica (Ur-Leica). Leica M cameras are still in production today. The M3 introduced several features to the Leica, among them the combination of viewfinder and rangefinder in one bright window, and a bayonet lens mount.

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There are many variants of M3s as there were changes made as new technology developed.
In terms of serial numbers here is a guide from Cameraquest
700,000 Starting Point (1953)

785,801 (1955) added Viewfinder Frame Selector Lever

844,001 (1957) glass film pressure plate changed to metal

919,251 (1958) Lever advance changed from two to single stroke. In use "single strokes" are generally much preferred, but some old timers are adamant that the "double strokes" are smoother and even last longer because each stroke puts less stress on the gearing.

919,251 (1958) Depth of field indicators placed in the Rangefinder. Notice the little cutouts on the upper and lower edges of the RF image. The cutouts indicate Depth of Field for 50mm lenses at f/5.6(larger lower cutout) and f/16(larger upper cutout). If the double rangefinder image is within the cutout, either in front of or behind the focused object, both objects will be sharp.

This new bayonet mount, which has not been changed in the following half century, is called the Leica M mount. Lenses are changed faster than with a screw mount, and framelines set automatically. Non-Leitz/Leica bayonet-mount lenses can also be used (although none were produced in any quantity while the M3 was sold), and a simple adapter also allows the use of screwmount lenses (whether from Leitz or other companies).

When compared to a Leica IIIf (the previous Leica release), the M3 has an exceptionally bright viewfinder. It has a high magnification factor, which is very useful in critical focusing. The M3 has a factor of 0.92×, while other Leicas use 0.85×, 0.72×, or less. Furthermore, it was the first Leica to combine rangefinder and viewfinder into one window. (Other cameras, such as the Contax II, already had this feature before the war; and other companies were making screwmount bodies with combined finders.) Framelines for 50, 90 and 135mm are shown, although none for any wider lenses. However, Leica solved this problem in two different ways. One was using a separate viewfinder slid into the accessory shoe. The other way is the use of so called Leica glasses; auxiliary lenses are put in front of the viewfinder and rangefinder windows for the 35mm focal length. The drawback of these glasses is they reduce the famed brightness of the finder.

The 50 mm framelines are always visible. The viewfinder image is slightly larger. There are two ways to select the 90mm or 135mm framelines. Putting a 90mm lens on the camera will automatically select the corresponding framelines. The other way is toggling a small lever on the left of the lens. This way, you can see the tele-framelines when using a 50mm lens. It helps you to visualize the field of view for another focal length.

Viewfinder cameras don't show the exact same image in the viewfinder and on the film. This parallax problem is compensated in the M3 by moving the framelines when you focus the lens. This parallax compensation has its limits, but in most practical situations, it works well.

Leica IIIF and its predecessors had used a knob to advance the film. For fear of tearing the film, early M3s had a double stroke advance lever, just as the Neoca 2S had. Later models had single-stroke levers, which speeded up operation of the camera. Another type of variation is in the film pressure plate used. Early models used a glass plate to keep the film flat, later models use a metal plate.

Earlier Leicas had used two rotating rings with separate slow and fast speeds, as on the Exakta Varex. The M3 combined slower and faster speeds and the dial doesn't rotate any more when firing. Supposedly, this reduces vibrations in the camera. Early models used a non-geometrical series of shutter speeds. On later models this became the international standard of 1s to 1/1000s.

Leica's model numbering scheme has often caused confusion among users and collectors alike. The next model introduced by Leica was the M2. This was a cost-reduced M3 with a different selection of viewfinder framelines (35, 50, and 90mm) and other changes suggested by professional photojournalists, who were Leica's primary customers at the time. The M2 was sold alongside the M3, and both continued production with minor changes until eventually replaced by the M4. The M1 was also based on the M3 body. The M1 had no rangefinder and was designed primarily to be mounted on a microscope or a telescope for use as a scientific instrument camera, though it could also be used as a general purpose scale-focus camera or with an external rangefinder.

All Leica M series cameras, even the radically redesigned M5, can be recognised by their basic resemblance to the M3 that started the series. Many consider the M3 to be the most beautiful Leica ever made. At the same time, the lack of wide-angle frame lines is sometimes regretted.